1. Field of the Invention
The present invention relates to a process for the preparation of a copper-zinc material having a small grain size, and is related to U.S. patent application Ser. No. 941,131 for Brass Material And A Process For The Preparation Thereof, filed Aug. 11, 1978 by the present inventor and commonly assigned herewith.
2. Discussion of the Prior Art
A process of this type has already become known from U.S. Pat. No. 2,676,123. In this known process, an alloy containing 5 to 40% by weight of zinc, with the remainder being copper as well as impurities, is initially cast and worked in a suitable manner, if need be, with intermediate annealing. The alloy is then annealed at 500.degree. to 600.degree. C. and thereafter cold worked without intermediate annealing. A final annealing at temperatures of about 375.degree. C. should be carried out for so long until the alloy is completely recrystallized whereby the grain size lies above 5 .mu.m.
This known process provides for a material which, due to its relatively fine-grained structure and its therefrom resultant mechanical properties, is well suited for specialized further processing applications, among which there is also the further cold working. Thus, this material can be plastically deformed with good results. Nevertheless, the structure of this known material is still not sufficiently fine-grained to also allow for superplastic deformations which are connected with extraordinarily extensive elongations. Furthermore, the fine-grain quality of the known material is still not adequate to afford the mechanical strength, fatigue strength, as well as corrosion resistance, at least with respect to most types of corrosives, required for many fields of application.
Additionally thereto, the material prepared in accordance with the known process, in the predominant range of the given alloy composition, namely at 5 to about 37% by weight of zinc, is present as a single-phase structure, in this case as an .alpha. phase. This .alpha. structure tends towards grain coarsening, particularly at temperature increases. This is also the reason due to which the carrying out of the known process is relatively problematic in actual practice. Even a minute exceeding of the annealing period can, in this instance, lead to a significant coarsening of the grain and as a result to an impairment in the mechanical properties.